Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous compounds and solid particulate matter, which may include unburned carbon particles called soot.
Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of particulates emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove the particulate matter from the exhaust flow of an engine using a particulate trap. A particulate trap is a filter designed to trap particulate matter in, for example, a mesh filtering media. During operation, the mesh filtering media of the particulate trap may saturate and clog with particulate matter. As a result, an undesirable exhaust system back pressure may develop.
To minimize or prevent exhaust system back pressure, the particulate trap may be subjected to a regeneration process in which some, most, or all of the trapped particulate matter may be removed from the filter. In one regeneration technique, an electric current may be passed through the mesh filtering media, which may include a metal, for example. In response to this current, the temperature of the filter may rise due to resistive heating. Ultimately, the temperature may be raised above the combustion temperature of the trapped particulate matter, and the particulate matter may be burned away from the filter.
Establishing a suitable electrical connection to the mesh of the particulate trap can be challenging. Particularly, the joint between the filter media and an electrical connector, which provides the current for regeneration, may be exposed to a harsh environment within the exhaust system. In this environment, the high temperatures and presence of corrosive compounds in the exhaust stream can promote corrosion and oxidation of the joint. Further, oxidation at the joint may even be facilitated by the porous nature of the filter media.
Oxidation of the joint and the surrounding mesh filter media can lead to the development of various oxide materials at the joint that can cause an increase in electrical resistance at the joint. As a result of the higher electrical resistance, there may be a disproportionate amount of localized heating occurring in the area of the joint. The mesh filter material can melt, which can further increase the resistance at the joint. Ultimately, an open circuit condition may result, which would prevent the flow of current to the filter media and, therefore, eliminate the capability of regeneration of the filter media through resistive heating. Thus, there is a need for an electrical connection to the filter of a particulate trap that can withstand the harsh environment within an exhaust system.
At least one method for forming a joint with a mesh filter media is disclosed in U.S. Patent Application Publication No. US 2004/0031748 (“the 748 patent publication”) to Kochert et al. The '748 patent publication describes a process of forming a joint between a filter medium and a supporting structure by welding the filter medium to the supporting structure.
Although the joint described in the '748 patent publication may be suitable for use in certain exhaust system applications, this type of joint may have several shortcomings. For example, the welding technique may require temperatures high enough to damage the mesh material. Melting of the mesh during the welding process may have the effect of severing conductive elements of the mesh, which could lead to increased electrical resistance at the joint. Thus, the welding process of the '748 patent publication may be unsuitable for forming an electrical connection to a filter media.
The present disclosure is directed to overcoming one or more of the problems of the prior art steam oxidation technique.